US 7125521 B2
A method of unblinding an alignment mark comprising the following steps. A substrate having a cell area and an alignment mark within an alignment area is provided. An STI trench is formed into the substrate within the cell area. A silicon oxide layer is formed over the substrate, filling the STI trench and the alignment mark. The silicon oxide layer is planarized to form a planarized STI within the STI trench and leaving silicon oxide within the alignment mark to form a blinded alignment mark. A wet chemical etchant is applied within the alignment mark area over the blinded alignment mark to at least partially remove the silicon oxide within the alignment mark. The remaining silicon oxide is removed from within the blinded alignment mark to unblind the alignment mark. A drop etcher apparatus is also disclosed.
1. A drop etcher apparatus, comprising:
a control unit;
a dispenser tube having:
an upper end;
a semiconductor structure;
and a lower tip proximate an upper surface of the semiconductor structure;
a chemical reservoir partially filled with a chemical within the dispenser tube; the chemical reservoir having an initial upper surface; and
a dispenser line comprising a pressurized gas connecting the control unit to the upper end of the dispenser tube, wherein the control unit controls a flow of the pressurized gas to dispense a predetermined amount of a drop of the chemical to remove blinded alignment marks of the upper surface of the semiconductor structure, wherein the predetermined amount of the drop is dispensed through the lower tip of the dispensing tube to the upper surface of the semiconductor structure by exertion of pressure from the gas flowing through the dispenser line to the initial upper surface of the chemical reservoir;
a filter interposed in the dispenser line through which the gas flows to filter the gas;
a pressure regulator interposed in the dispenser line through which the gas flows to regulate the pressure of the gas; and
a high-speed shut-off valve interposed in the dispenser line through which the gas flows to regulate the flow of the gas, wherein the high-speed shut-off valve has a radius, and wherein the pressure regulator, the high speed shut-off valve, and the filter are external to the control unit;
wherein the upper surface of the semiconductor structure comprises an alignment mark area and a cell area, wherein the alignment mark area is spaced apart from a shallow trench isolation opening of the cell area, and wherein the lower tip of the dispensing tube is aligned with the blinded alignment marks of the alignment mark area.
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This is a division of patent application Ser. No. 10/353,229, filing date Jan. 28, 2003 now U.S. Pat. No. 6,746,966, A Method To Solve Alignment Mark Blinded Issues And Technology For Application Of Semiconductor Etching At A Tiny Area, assigned to the same assignee as the present invention, which is herein incorporated by reference in its entirety.
The present invention relates generally to semiconductor fabrication and more specifically to alignment marks and semiconductor etching at tiny areas.
Alignment marks are used to permit precise alignment of photolithographic masks with the wafer during masking steps to minimize misalignment between multiple layers. However, the alignment marks are ‘blinded’ after non-ODR shallow trench isolation (STI) chemical mechanical polishing (CMP) processes. This prevents transfer of the lower alignment mark to the next, upper layer, for example a metal layer.
An additional photolithography and etching step (ODR) are required to clear out the silicon oxide residue from the ‘blinded’ alignment mark field. This increases costs, increases the cycle time and manufacture loading. Further, the ODR approach is limited by the circuit design rule especially as the design rule passes 0.1 μm logic and beyond.
Blind alignment marks will become a critical issue in non-OD reverse tone photo/etch (ODR) processes after 0.1 μm and beyond shallow trench isolation (STI) CMP.
U.S. Pat. No. 6,194,287 B1 to Jang et al. describes an STI process and reverse mask to clear off alignment marks.
U.S. Pat. No. 6,080,635 to Jang et al. describes discloses a method to preserve alignment marks with STI processes.
U.S. Pat. No. 6,043,133 to Jang et al. describes a process to improve STI removal over alignment marks.
U.S. Pat. No. 6,015,744 to Tseng describes a clear out and alignment mark process.
U.S. Pat. No. 5,188,258 to Iwashita describes a quantitative fluid discharge device.
Accordingly, it is an object of one or more embodiments of the present invention to provide an improved method of unblinding alignment marks.
Other objects will appear hereinafter.
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a substrate having a cell area and an alignment mark area is provided. The substrate having an alignment mark within the alignment mark area. An STI trench is formed into the substrate within the cell area. A silicon oxide layer is formed over the substrate, filling the STI trench and the alignment mark. The silicon oxide layer is planarized to form a planarized STI within the STI trench and leaving silicon oxide within the alignment mark to form a blinded alignment mark. A wet chemical etchant is applied within the alignment mark area over the blinded alignment mark to at least partially remove the silicon oxide within the alignment mark. The remaining silicon oxide is removed from within the blinded alignment mark to unblind the alignment mark. A drop etcher apparatus is also disclosed.
The present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:
The inventors have discovered a novel method to solve the alignment mark (AM) blinding issues that includes using a wet chemical solution to partially remove the oxide residue within the blinded alignment marks after STI CMP processing. Furthermore, the wet chemical solution oxide residue removal easily integrates into the subsequent silicon nitride (Si3N4 or SiN) strip step.
As shown in
Alignment marks 16 have a depth of preferably from about 1150 to 1250 Å and more preferably about 1200 Å. Alignment marks 16 have a width of preferably from about 7.8 to 8.2 μm and more preferably about 8.0 μm.
A shallow trench isolation (STI) opening 14 is formed through the SiN layer 12 and into silicon substrate 10 within cell area 18 that is spaced apart form alignment mark area 20.
Formation of Oxide Layer 22
To form the STI, a silicon oxide (oxide) layer 22 is formed over silicon substrate 10, filling STI trench 14 and alignment marks 16. Alignment marks 16 are filled by oxide layer 22 and by the oxide residue formed by the CMP of oxide layer 22 to form planarized STI layer 22′ (see below).
Planarization of Oxide Layer 22
Oxide layer 22 is then planarized, preferably by a chemical mechanical polishing (CMP) process to form planarized STI 22′ and filling (and ‘blinding’) alignment marks 16 with oxide 22″.
Use of Drop Etcher 40
As shown in
Wet etching chemical 25 is preferably hydrogen fluoride (HF) or buffered oxide etchant (BOE). If BOE is used, it has an oxide:SiN etching sensitivity of about 10:1 with an oxide etching rate of about 1400 Å/min. If HF is used, it has an oxide:SiN etching sensitivity of about 15:1 with an oxide etching rate of about 9000 Å/min.
As shown in
Line 51 connects control unit 30 to the upper portion of dispenser tube 34 and through which line 51 a gas, such as preferably air or nitrogen (N2), is pulsed through a filter 60, a pressure regulator 62 and a high-speed shut-off valve 64 controlled 66 by the controller 30 or a timer.
The time control is preferably from about 0.001 to 10.000 seconds and more preferably from about 0.001 to 5.000 seconds; the pressure control is preferably from about 0.001 to 10.000 psi and more preferably from about 0.001 to 5.000 psi; the tip 24 inside diameter 54 is preferably from about 0.01 to 2.00 mm and more preferably from about 0.10 to 1.00 mm; and the dispenser distance 70 is preferably from about 1.0 μm to 1.0 cm and more preferably from about 0.5 to 6.0 mm.
As illustrated in
By the precise control of the gas pressure, time and size of the tips and nozzles involved, consistent deposits are ensured with a sped-up output while maintaining high quality and reduced waste. By increasing either the gas pressure, the time duration or the tip gauge (inside diameter 54), the size of the drop and hence the etch size will increase.
The tip 24 is preferably comprised of a non-reactive material such as polytetrafluorethylene (PTFE), perfluoroalkoxy (PFA), or polyvinyl chloride (PVC). For wet dip process optimization, the tip 24 preferably has: an outer diameter 56 of preferably from about 0.5 to 3.0 mm and more preferably about 1.0 mm; and an inner diameter 54 of preferably from about 0.5 to 0.7 mm and more preferably about 0.5 mm.
The tip 24 is preferably spaced from the upper surface of the structure 10 a dispenser distance 70 of preferably from about 1 μm to 1 cm and more preferably from about 0.5 mm to 6.0 mm.
In real process control, the drop 26 has an inner diameter 100 of from about 0.1 to 0.7 mm and an outer diameter of from about 1.0 to 3.0 mm (see
Etching of Oxide 22″ Within Alignment Marks 16
As shown in
The remainder of drop 26 is removed before the SiN strip step (see below).
SiN Layer 12 Strip
As shown in
Thus, alignment marks 16 are now clear and transparent to the next formed layer, such as a metal layer, so that the alignments marks 16 are transferred to the upper, next formed layer and may be readily observed for continued fabrication.
Advantages of the Present Invention
The advantages of one or more embodiments of the present invention include:
While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.